RSV is the leading cause of acute lower respiratory tract infections in children, causing an estimated 33 million new infections each year. Despite this significant global burden, there is no RSV vaccine and there are currently limited therapeutic options for severe RSV infection. Vaccine efforts have been hindered by 1) failure of early vaccine attempts using formalin-inactivated RSV (FI-RSV) which led to the occurrence of enhanced respiratory disease (ERD) in some infants and 2) deficiencies of rodent models that do not to recapitulate critical aspects of human infant RSV infection. Studies have shown that vaccination with FI-RSV and subsequent RSV challenge skews Th2-cell mediated responses towards immunopathology, while prior exposure to live virus properly primes the adaptive and innate immune systems without ERD. Consequently, the potential for subunit and inactivated RSV vaccines to cause ERD remains a particular concern for RSV nave pediatric population. In this proposal, we offer a novel immunization strategy in a highly relevant, pre-clinical model of RSV that addresses these barriers to vaccine development. We propose to test novel maternal immunization strategies for eliciting protective maternal immunity and test the protective efficacy of passive transfer of neutralizing antibodies. We hypothesize that this approach will provide protective passive immunity in infants during perinatal period of greatest RSV susceptibility. We propose to test this approach in a non-human primate model of RSV infection using recombinant virus-like particle (VLP) vaccines expressing F antigen in appropriate conformation. In addition, we will use this immunization strategy to improve understanding of critical aspects of maternal immunization including 1) the effects of pregnancy on vaccine-induced immunity 2) the kinetics of maternal transfer of neutralizing antibodies responses and 3) the efficacy of maternal immunization and protection in a clinically relevant infant primate model. In addition, we will define innate and adaptive immune correlates of protection in RSV infection in adult macaques, information that will be critical to the understanding of deficiencies in the infant lung environment. We expect these studies will have a catalytic effect on the RSV field by establishing a pre-clinical model of infection for design and testing maternal immunization strategies as well as in a highly relevant, pre-clinical model that most closely mimics human disease.